Edexcel iGCSE Physics -3.29P Loudness and Amplitude- Study Notes- New Syllabus

Loudness and Amplitude of Sound

Loudness describes how loud or quiet a sound is perceived by the human ear. The loudness of a sound depends on the amplitude of vibration of the sound source.

Amplitude and Loudness

Amplitude is the maximum displacement of particles from their rest position during vibration.

• Large amplitude → loud sound
• Small amplitude → quiet sound

The greater the amplitude of vibration of the source, the louder the sound produced.

Source of Loud Sounds

• Sound is produced by vibrating objects.
• Vibrations with greater energy produce larger amplitudes.
• More energy is transferred to the surrounding air.

For example, striking a drum harder produces a louder sound.

Wave Relationship

Sound waves obey the wave equation:

\( \mathrm{v = f\lambda} \)

Although this equation does not include amplitude, amplitude affects the energy carried by the wave.

Important Distinction

• Loudness depends on amplitude.
• Pitch depends on frequency.
• Changing amplitude does not change frequency.

Representation on an Oscilloscope

• Louder sound → taller waveform on the screen.
• Quieter sound → shorter waveform.
• Spacing between waves remains unchanged if pitch is constant.

Key Idea

• Loudness is related to energy of vibration.
• Amplitude measures the strength of vibration.
• Greater amplitude means more energy.

Important Points to Remember

• Loudness is a perception.
• Amplitude is a measurable quantity.
• Human ears detect larger amplitudes as louder sounds.